To identify the base of the original expression before the change of base formula was used, we need to examine the expression you provided:
\[ \frac{\log_2 128}{\log_2 32} \]
Using the change of base formula, we know that:
\[ \log_a b = \frac{\log_c b}{\log_c a} \]
For the given expression, it can be re-expressed in terms of a different base \(c\):
\[ \frac{\log_c 128}{\log_c 32} \]
Here, both logs are using the same base \(c\). Based on the structure of the expression, we can ascertain that the original base before the application of the change of base formula is \(2\).
Thus, the base of the original expression was
\[ \boxed{2} \]